The present invention relates to an electrophotographic color toner (hereinafter, is sometimes referred to as simply xe2x80x9ctonerxe2x80x9d) used for instruments utilizing an electrophotographic process, such as a copying machine, a printer, a facsimile, etc., and particularly, for a color copying machine; an electrophotographic developer; and an image-forming process.
As an electrophotographic process, various processes, from the processes described in Japanese Patent Publication No. 42-23910 (1967), etc., have hitherto been known. In an electrophotographic process, an electrostatic latent image is electrically formed on a photoreceptor utilizing a photoconductive substance by various means, the latent image is developed using a toner, after transferring the toner image on the photoreceptor onto a transfer material such as a paper, etc., using or without using an intermediate transfer material, the transferred image is fixed by heating, pressing, heat-pressing, a solvent vapor, etc., to form a fixed image through the above-described plural steps. The toner remained on the photoreceptor is, if necessary, cleaned by various methods, and the above-described plural steps are repeated.
Recently, with the development of instruments in an information-oriented society and the repletion of a communication network system, such an electrophotographic process has been widely used not only for copying machines but also printers and also a color-image formation by an electrophotographic process has been rapidly advanced. With the propagation of color copying machine and printer (hereinafter, a copying machine and a printer are generally referred to as xe2x80x9ccopying machinexe2x80x9d in this invention), a black and white copying machine is being unable to be distinguished from a color copying machine, and the using way of forming both a black and white copy or print and a color copy or print by a same color copying machine has been increased.
In the case of, as a matter of course, black and white images and, particularly, in the case of color images, it has been strongly required that the images formed have a high image quality and a high coloring. In order to obtain an image of a high image quality and a high coloring, from the view points of a light transmittance, a glossiness, etc., it is required that a toner is sufficiently melted and the surface of the image after fixing is smooth. For the reason, as a toner for a color electrophotography of prior art, a resin which has a low molecular weight and is relatively sharply melted from a glassy state to lover the melting viscosity is used, and as a fixing step, a contact-type heat-press fixing system excellent in the thermal efficiency, the reliability, and the safety has been used.
However, because the toner using a such a resin is sharply melted, the melting viscosity thereof is changed susceptibly to the temperature change at fixing. Also, because the melting viscosity at fixing must be lowered, the toner has a fault that the permeation of the toner among the fibers of a paper mainly used for image recording occurs (hereinafter, is referred to as xe2x80x9cpenetration phenomenonxe2x80x9d) and the image formed is deteriorated. Accordingly, to obtain an image having a high image quality in a color copying machine of prior art, it is required to use a specific paper for color copying, which has a coating layer or has a relatively dense space between the fibers to be able to reduce the penetration phenomenon.
However, when it becomes possible to form both a black and white copy and a color copy by a same color copying machine as described above, it has been desired to be able to use a paper which has hitherto been used for a black and white copying machine (hereinafter, is referred to as xe2x80x9cplain paperxe2x80x9d) for the color copy. Because a plain paper has a small heat capacity of the paper itself as compared with a paper for color copying, the amount of heat added to a toner at fixing is increased, which rends to lower the melting viscosity of the toner than the melting viscosity at fixing in a paper for color. Further, there newly occurs the problem that because the space between the fibers of the plain paper is rough (not dense), the penetration phenomenon of a toner remarkably occurs to deteriorate the image formed. When the penetration phenomenon occurs, because the diameter of the fibers used for a plain paper is several tens m and the diameter of about the size of the space between the fibers, the image deterioration is sufficiently visually detected as the irregularity of image. About the deterioration of image by the penetration phenomenon, considering from that even in, for example, a printing technique and an ink jet technique, oozing of a printing ink or an ink for ink jet is prevented by using a specific paper having formed an image-receiving layer, such as a coated paper, a silica-coated paper, etc., it is sure that the solution is difficult. However, it is important to utilize the excellent convenience of the plain paper aptitude of a black and white copying machine and to provide a high image-quality technique without need of selection of paper in color copying.
Moreover, for the further requirement of forming images of a higher image quality, there is an attempt of thinning the image thickness of a fixed image. The image thickness of an electrophotographic image of prior art in from 5 to 7 xcexcm per one color and in the case of a full color, the image thickness reaches 20 xcexcm, whereby the difference in image thicknesses between a dense portion of an image density and a thin portion of an image density gives a sense of incongruity to observing persons. On the other hand, the image thickness of a printed image, which is a typical image having a high image quality, is few xcexcm even in full color and the printed image does not give a sense of incongruity as described above. Thus, in an electrophotographic image, it has been attempted to reduce the particle sizes of a toner to obtain a high resolving power, whereby a high-quality image similar to the printed image is obtained. However, to the printed image using a coated paper, in the case of an electrophotographic image using a paper having greatly lower surface smoothness than that of the coated paper, which the image thickness becomes thin, the above-described image deterioration becomes more liable to occur. Because the image deterioration described above is seen as white spots in the image and particularly when a wide area is occupied by a same density, a very unpleasant feeling is given, the improvement has been strongly desired.
A method of directly preventing the occurrence of such a penetration phenomenon of toner has not yet been proposed but many techniques having similar effects have been proposed.
For the purpose of realizing both low-temperature fixing and an offset resistance by incorporating fine particles in a toner to reduce the changing ratio of the melting viscosity of the toner to a temperature, Japanese Patent Laid-Open No. 6-332247 (1994) discloses a resin for toner wherein a polyester resin having a number average molecular weight of from 1000 to 5000 and an acid value of from 10 to 50 mg KOH/g is used as matrix and crosslinked resin particles having a mean particle size of from 0.05 to 2.0 xcexcm is used the domain. By the method, the melting viscosity curve is surely improved but when particles having a large mean particle size are incorporated, the occurrence of the penetration phenomenon of the toner cannot be prevented as well as the glossiness of the image is not obtained and the coloring property is lowered. Also, in the above-described patent publication, there are no descriptions about the dispersibility of the particles and when the dispersibility is inferior, the occurrence of the penetration phenomenon cannot be prevented. Furthermore, because for mixing the particles and the binder, a solvent is used, it cannot be avoided that the particles, which are a resin, are dissolved or swelled. Thereby, the particles are aggregated or it is necessary to dry the particles at a high temperature to remove the solvent in the particles, whereby it sometimes happens that the particles are aggregated in the drying step and the heat deterioration of the resin by temperature occurs. When the particles are aggregated, there occur the problems that it becomes difficult to prevent the occurrence of the penetration phenomenon and the heat deterioration reduces the toner characteristics such as the electrostatic charging property, etc.
Also, Japanese Patent Laid-open No. 8-220800 (1996) discloses a toner wherein inorganic particles are incorporated in toner binders and the viscoelastic characteristics of each color are made same as those of a black toner to improve the offset resistance. By the method, the melting viscoelastic curve of the toner can be surely improved in the measurement of the viscoelasticity data, but in a high-speed copying machine requiring a high speed, a high image quality, and high coloring, the effect is scarcely obtained for the offset resistance. This is because the state of the toner during the measurement of the viscoelasticity is utterly different from the state of the toner during fixing. Also, when the dispersibility of these particles is inferior, the occurrence of the penetration phenomenon cannot be prevented. Moreover, when the addition amount of the inorganic particles is from 1 to 10 parts by weight, the prevention of the occurrence of the penetration phenomenon occurring from a higher viscosity than a hot offset is insufficient.
As described above, it is difficult to prevent the occurrence of the penetration phenomenon of a toner into a plain paper by using the above-described techniques of prior art, and a toner newly designed has become necessary at present.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-described problems in the techniques of prior art and an object of this invention is to provide an electrophotographic color toner which has a broad fixable temperature region of the toner and does not cause an image deterioration by preventing the occurrence of the penetration phenomenon to a paper while keeping a high image quality and high coloring even by using paper other than a paper for color copy without deteriorating various characteristics of a toner of prior art, and also to provide an electrophotographic developer using the toner and an image-forming process using the developer.
As the result of various investigations by paying a specific attention to not only the melting viscoelasticity of a toner but also a fixing member (a transfer material), particularly the characteristics of a paper, such as the unevenness of the fibers of a paper and the surface characteristics of a paper, the present inventors have discovered that by incorporating fine particles in a toner in a specific state, an image having a high image quality and high coloring can be maintained and also the occurrence of the penetration phenomenon of a toner into a paper can be restrained and have accomplished the present invention.
That is, the first aspect of this invention is an electrophotographic color toner containing at least a coloring agent, a binder resin, and light color or colorless fine particles, wherein the toner particles containing fine particles having particle sizes of at least 1.0 xcexcm as said fine particles do not constitute more than half of the total toner particles.
The second aspect of this invention is an electrophotographic color toner containing at least a coloring agent and a binder resin, wherein the dynamic complex elastic modulus G*(distortion ratio 100%, frequency 10 rad/sec.) of the toner measured at a temperature at which the dynamic complex elastic modulus G*1 (distortion ratio 100%, frequency 10 rad/sec.) of said binder resin becomes 1000 Pa is from 3000 to 50000 Pa.
The third aspect of this invention is an electrophotographic developer containing at least a toner, wherein said toner is the electrophotographic color toner described in the above-described first or second aspect
The fourth aspect of this invention is an image-forming process including a step of forming an electrostatic latent image on a latent image support, a step of developing the latent image using an electrophotographic developer to form a toner image, a step of transferring the developed toner image onto a transfer material, and a step of fixing the toner image on the transfer material, wherein said electrophotographic developer is the electrophotographic developer described in the above-described third aspect, and the surface smoothness of the transfer material is 80 seconds or lower.
The fifth aspect of this invention is an image-forming process including a step of forming an electrostatic latent image on an electrostatic latent image support, a step of forming a toner image by developing the electrostatic latent image using an electrophotographic developer, a step of transferring the developed toner image onto a transfer material, and a step of fixing the toner image on the transfer material, wherein said electrophotographic developer is the electrophotographic developer described in the above-described third aspect, and the step of fixing the toner image on the transfer material is carried out using a heat-contact-type fixing apparatus.